Dual functional zeolite/hydroxyapatite nanocomposite for highly effective removal of malachite green dye and cadmium from wastewater

Abstract Water scarcity and contamination demand efficient wastewater treatment technologies that are both effective and sustainable. In this study, a waste‑derived zeolite/hydroxyapatite nanocomposite (W‑ZEO/HAP‑NC) was synthesized from rice‑husk‑derived silica and aluminum‑can waste and evaluated for its versatile, dual-functional capacity to remove both Cd(II) and malachite green (MG) from water. XRD, SEM–EDX, FTIR, zeta potential and BET analyses confirmed a porous W‑ZEO/HAP‑NC framework enriched with hydroxyl, phosphate, and silicate groups that supply abundant adsorption sites. Batch experiments showed rapid, pH‑dependent uptake, with equilibrium and kinetic data best described by the Freundlich and pseudo‑second‑order models. Under optimized conditions, W‑ZEO/HAP‑NC achieved Langmuir capacities of 666.7 mg g − 1 for Cd(II) and 400.0 mg g − 1 for MG, driven by electrostatic attraction, ion exchange, surface complexation, π–π interactions, and hydrogen bonding. The composite retained 85–95% of its initial efficiency after four adsorption–desorption cycles, underscoring its potential as a high‑capacity, regenerable adsorbent for wastewater purification and waste valorization.